A live axle roll up door is a door made of a flexible material, or having hinged segments, that raises and lowers by means of a rotating axle located above the door frame. The door is typically attached at an end to a set of drum wheels that rotate with the axle. As the axle rotates, the door rolls up onto the drum wheels. If the direction of rotation of the axle is reversed, the door rolls off of the drum wheel and travels downward to close. In warehouses and mini-storage facilities it is common to place a live axle roll up door at the opening to the building. These doors are usually relatively lightweight and designed to be easily and quickly retracted either manually or automatically.
In order to allow for manual operation of the door, a coil spring is usually installed at the top of the door to counterbalance the weight of the door. The  coil spring is usually disposed around a shaft and fixed to the shaft at one end, such that the spring rotates with the shaft, and fixed to a stationary structure at the other end. The torsional forces created in the spring by the rotation of the shaft provide a variable torque which counteracts the weight of the door. As the door is lowered, the torsional forces developed in the spring pull in the opposite direction of the travel of the door. The amount of tension resulting from the torsional forces generated in the coil spring will determine the performance characteristics of the door.
If there is too little tension, the weight of the door may cause the door to drift down from the open position to the closed position. If the tension is too great, the door may be hard to pull down and it may not stay closed. Also, a door with too much tension in the spring will fly up upon exertion of an upward force to open the door. If the amount of tension is set correctly, the door can be lowered gently and a balance will be struck between the weight of the door and the force exerted by the spring. At certain positions, the weight of the door may balance with the force of the spring and the door can be left partially open. In the closed  position, the weight of the door will overcome the force of the spring and the end of the door will rest on the ground. Also, if the door is adjusted properly, a small amount of upward force will release the potential energy of the spring and the door will easily travel in the vertical direction.
The live axle is free to rotate within and is supported by brackets on either side of the opening of the door. On one end of the axle, a tension bracket connects to one end of the spring. The other end of the spring is attached to a drum wheel that rolls the door. The drum wheel rotates with the axle and the end of the door is attached to the drum wheel. As the axle turns, the door, which is constructed of a sectional material that is flexible enough to roll up, rolls onto the drum wheels.